Coupled inductor dc step down converter

Abstract

A step down power converter include a switch, an inductor, a diode, a capacitor, and a winding magnetically coupled to the inductor. The diode, the inductor and the capacitor are coupled in series, and the transistor, the coupled winding and the capacitor are coupled in series. An output voltage Vout is supplied across the capacitor. When the switch is ON, energy is transferred from an input supply voltage to a load coupled across the capacitor, and current flows through the coupled winding thereby storing energy in the winding. When the switch OFF, current does not flow through the coupled winding, but the energy stored in the winding induces current in the magnetically coupled inductor, thereby delivering energy from the winding to the load.

What is claimed is: 
     
         1 . A power converter circuit to convert an input voltage to an output voltage, the power converter comprising:
 a. a diode;   b. a first inductor coupled in series with the diode;   c. an output capacitor coupled to an input supply voltage and coupled in parallel to the serially coupled diode and first inductor, wherein the output voltage is a voltage across the capacitor;   d. a second inductor coupled in series to the capacitor, wherein the second inductor is magnetically coupled to the first inductor; and   e. a switch coupled in series to the second inductor and the input supply voltage.   
     
     
         2 . The power converter circuit of  claim 1  wherein the power converter circuit is configured to transfer energy from the input supply voltage to a load coupled to the capacitor and to store energy in the second inductor when the switch is ON. 
     
     
         3 . The power converter of  claim 2  wherein the power converter is configured to transfer energy from the second inductor to the load coupled to the capacitor when the switch is OFF. 
     
     
         4 . The power converter of  claim 1  wherein the diode is reverse-biased and no current flows through the serially coupled first inductor when the switch is ON. 
     
     
         5 . The power converter of  claim 4  wherein current through the second inductor rises linearly to a peak value when the switch is turned ON. 
     
     
         6 . The power converter of  claim 1  wherein the diode is forward-biased and current flows through the serially coupled first inductor when the switch is OFF. 
     
     
         7 . The power converter of  claim 6  wherein current through the first inductor decreases linearly when the switch is turned OFF. 
     
     
         8 . The power converter of  claim 1  wherein a cathode of the diode is coupled to a high side of the input supply voltage and to a first terminal of the capacitor, an anode of the diode is coupled to a first terminal of the first inductor, and a second terminal of the first inductor is coupled to a second terminal of the capacitor. 
     
     
         9 . The power converter of  claim 8  wherein a first terminal of the second inductor is coupled to the switch, and a second terminal of the second inductor is coupled to the second terminal of the capacitor. 
     
     
         10 . The power converter of  claim 1  wherein the switch is coupled to a low-side of the input supply voltage. 
     
     
         11 . The power converter of  claim 1  wherein the switch comprises a transistor. 
     
     
         12 . The power converter of  claim 1  further comprising a controller coupled to the switch. 
     
     
         13 . A power converter circuit comprising:
 a. a buck type converter including a diode, a capacitor, and an inductor, wherein the buck type converter is coupled to an input supply voltage and supplies a stepped-down output voltage across the capacitor;   b. a winding coupled in series to the capacitor and magnetically coupled to the inductor; and   b. a switch coupled in series to the coupled winding and to a low-side of the input supply voltage.   
     
     
         14 . The power converter of  claim 13  further comprising a controller coupled to the switch to turn the switch ON and OFF, wherein the power converter circuit is configured such that when the switch is ON current flows through the winding and not the inductor, thereby storing energy in the winding and delivering energy from the input supply voltage to a load coupled to the capacitor, and when the switch is OFF current flows through the inductor and not the winding, whereby the stored energy in the winding induces current in the inductor thereby delivering energy from the winding to the load coupled to the capacitor.